Embossing calender



atentefci Sept. 253, 195.2

EMBos'siNG CALENDER Taulf. -I1lner, Hamilton, Ohio, assigner to The Champion `Paperand V'Fibre lCom-pany, `liamiii ton, vCbhimpa 'corporation of `,Ohio

Application omheen, 194e, serial No. tosses (o1. ini-ess) .-2 Claims.

This invention relates to embossing processes and embossing calenders 'and has for itsprimary objects the provision of methods and apparatus whereby a paper' web can be embossed on both sides in a single passage through `the calender, whereby the embossing on the-two sides can 'be made -of substantially equal intensity, whereby the relative lintensity vof the "impressions on the opposite sides of the web ican be readily adjustedand whereby the aforesaid objects can -Vbe accomplished in a calender comprisinga single staclr'of` rolls wherenthe drive is applied to only asingle roll and wherein wthe embossing vpres-- sureis applied through vthe journals of only a single roll.

In the past 4the machines most l generally used for embossing paper were two-roll calenders wherein the paper was embossed between an engravedsteel rolland a roll having a yielding surface composed, usually, of compressed paper. The Vdiameter of the compressed paper roll is commonly twice, though occasionally it `is some other exact multiple, of that of the engraved roll.` When the paper Vis'to Vbe embossed clear through, the Vrolls are Ageared together so that the pattern becomes impressed in the paper roll. When it vis desired to emboss only the surface, as when both sides are to be embossed, the gearing is omitted and-a uthird `roll with a smooth metallic surface is lsometimes run against Ythe y opposite side of the compressed paper roll to iron out any impressions found on vthe surface of the-paper roll by the embossing opera-tion.

In order to emboss both sides of a web it has been Ithe usual practice -to run it through `the machine a second time with the opposite rside against the engraved roll. 'In'this second passage Ythrough thefmachine, the previously -embossed surface is Apressed against the Vrelatively smooth surface of --the compressed 4fier roll, which partially presses out Vthe pattern on -that surface of the web, while thefpattern is-impressed to full vdepth on lthe second surface. In order to secure approximately the same depth of lmprcssing on the opposite side ofthe embossed paperand avoid thedefectv known as twosidedness, -the .embossing pressure must be .greatly reduced in embossing the-second side, commonly to between sixtyfand eighty percent ofsthatused in `embossngthe iirstzside. By thsmeans'both the `depth of the second impression andthe degree of pressing out of the iirst impression are reduced and the depthof impression on Vthersecond-side andof :the residual :impression on the rst :side can `be made substantially-equal.

The pressure required `for embossing depends upon'V an imperfectly understood rvcombination Aof i the desired depth of embossing, the type and A depth of the Vpattern on the engraved roll, the diameter ofthe engraved metal embossing roll, the diameterV and hardnessV of the cooperating fiber embossing roll, the speed Yof-ti1e-paper web through the embosser, the temperature fand moisture content, aswellasl-thethickness, hardness, and composition ci the body and of #each of the opposite surfaces -of-the paper-web, the humidity andftemperature of theatmosphere', the temperature of the embossing rolls, etc., etc. The pressure required f or embossing the lsecond side depends onthe same-set vrof factors and-also on the degree to which the first side was em bossed. `.ln this connection it should be vnoted that the factors are, -n general, not all the same when embossing the'second side as when-embossr ing vthe vfirst side, yand lthat one or more factors willhave to be adjusted if Ythe same depth-of impression is desired enea-ch sideeof the web.

vlVIachinres vhave in -the'past been -proposed for embossing both sides of -a-paper web. vSo far as I am aware, however, these have always incorporated two separately driven-sets lof embossing rolls and two separate and independently adjustable pressure applying-devices VAto per-mit vthe aforesaid adjustment of the relative depth of pattern on the oppositesidesof the sheet. Such machines are in leect two lseparate embossing calenders arranged in tandem, yirrespective of the actual relative vpositions of the two -sets voi rolls. They donot-serveto accomplish'the obu jects accomplished bythe Apresent invention.

I have now vdiscoveredthat l can .emboss .a paper weben both sides kin-a singleioperation on a-single machine wherein the power is applied to only one roll and the embossing pressure is appliedto the journals vkof `only one roll, and that I-can-control-the operation to give/substantially the same depth of impression :on each -side of the 'finished web. For lthis purpose I have found it possibleto use-a single-stack or calender rolls supported -on the journals-of the-lowermostV roll and pressed'together -by pressure applied to thejournals Vof the uppermost `roll, wherein' vthe rolls are driven by power applied-toV only one yof the rolls,most Vcommonly the bottom roll.

I have-also' discoveredthat if, in passing once through such alstack, a paper ,web .berst-.embossedon one side by an lengravedroll of austral diameter, and ythen embossed on the otherside by an engraved roll of materially larger diameter (say from two to three times that of the roll used to emboss the first side) it is possible, for embossing the second side, to use pressure per unit of roll length which is as great as or greater than that used for embossing the second side, without making the impression on the second side more prominent than that on the first side. This is believed to be due to a larger area of contact between the larger engraved roll and the yielding surface of the cooperating nonmetallic roll, resulting in a lower pressure per unit area of contact, which appears to give the same result as the lower applied pressure used to emboss the second sidein customary embossing processes. I have further found it possible, if the second side is embossed by a roll of materially larger diameter than that used to emboss the first side, to adjust the relative intensity of the embossing on the opposite sides of the finished web, by merely adjusting the pressure applied to the journals of the uppermost rollthus simultaneously increasing or decreasing the embossing pressure of the smaller roll on the first side of the web and that of the larger roll on the second side of the web, by the same amount. I have further discovered that, if the range of this adjustment is not adequate to completely equalize the impressions of any specific pattern on the opposite sides of a web of paper of any specific character, thickness, and condition, the substitution of a harder or softer compressed fiber roll against the first or second engraved roll, as required, will serve to shift the range of variation of two sidedness with variations of applied pressure to a degree such that it will be possible to eliminate two-sidedness by mere adjustment of the pressure.

More specifically I have discovered that, in a single two-side embossing calender of the type described, if the roll embossing the second side is made materially larger in diameter than that embossing the first side, an increase in the pressure applied through the journals of the uppermost.

roll serves, for a combination of reasons not clearly understood, to increase the final effect of the impression on the second side to a greater degrec than it increases the final effect of the impression on the first side, and that the simultaneous equal change in pressure in both embossing nips will therefore serve to differentially adjust the final intensity of impression on the opposite sides. I have discovered further that within the limits commonly used, the change in relative intensity of the impressions caused by this adjustment is more apparent than any change `in absolute intensity caused by the same adjustment, so that the only noticeable effect of the pressure adjustment is a change in relative intensity of the pattern on the opposite sides of the web.

It has been stated that the engraved roll used to emboss the second side should be materially larger than that used to emboss the first side. I have successfully used one of double the size but less than that is not ordinarily satisfactory. Limitations of the pattern make it impossible to select any arbitrary dimension for the second roll. For example. if the pattern repeats itself twice around the circumference of the first roll, the selection of diameters for the second roll is limited to exact multiples of one half the diameter of the first roll. If the pattern repeats only once in the circumference of the first roll, the selection of diameters for the second roll is limited to multiples of the diameter of the first roll. Considerations of the depth of embossing would usually dictate a roll from two to three or more times the diameter of the rst roll. Considerations of cost make it desirable that the roll be no larger than necessary. On the other hand, particularly where the second roll is to be the lowermost roll in the stack, the diameter should be great enough, in proportion to the length, that the roll will not deflect to a harmful degree under the pressures required for embossing, which depend as is well understood on the type of pattern and on the material to be embossed. If it is necessary to make the roll larger, for the sake of stiffness, than is required for the purposes of this invention this may be compensated by making the cooperating compressed fiber roll smaller and harder than that cooperating with the rst roll. On the other hand if its size is inadequate to leave the impression on the first side of the desired depth, it may be compensated to some extent by making the cooperating fiber roll larger and softer than that cooperating with the first roll. For example, if the fitting of the pattern and other considerations make it desirable that the second engraved roll be twice the diameter of the first it is ordinarily desirable that the yielding-surfaced roll contacting the larger engraved roll be somewhat larger and/or softer than that contacting the first engraved roll.

If the selections are made as decribed it will be possible, by adjusting the applied pressure, to prevent two-sideness in the embossed web. Further, a web equally embossed on the two sides can be produced in a single operation on a single calender stack with a single pressure applying mechanism and a single power drive connection.

The method of driving the machine is, I find, also of great importance. As will be well understood by those familiar with supercalendering practice, the driving of the roll, not too near the top, in such a stack or rolls, serves to drive all rolls in the stack by friction. In the present invention, wherein the web passes through two embossing nips, the drive should be applied to a roll nearer to the nip where the second side is embossed than to that where the first side is embossed, and is advantageously applied directly to the second (i. e., the larger) engraved roll. In usual supercalendering practice the drive is normally applied to the lowermost roll or to the third roll from the bottom of the stack, and in the present invention the larger engraved roll is advantageously placed in one of these positions in the stack and then advantageously serves as the driving roll.

The invention will be better understood by reference to the accompanying drawing in which the single figure diagrammatically illustrates one widely applicable embodiment of the invention.

Referring to the drawing, it will be seen that in this, one of the simplest embodiments of my invention, the calender comprises six rolls, including a smooth surface metallic top roll l0 to the journals of which any required degree of pressure can be applied by any suitable pressure device as, for example, a pair of hydraulic cylinders indicated diagrammatically at Il the pressure in which is controlled by any suitable known type of fiuid pressure control devices. The pressure applying and controlling devices are all of known types. Their particular construction and arrangement form no part of the present invention and will not be further described. Below roll III is a yielding-surfaced roll l2 having a surface composed advantageously of compressed ber. Next is an engraved metallic roll I3 which is followed by two yielding-surfaced rolls i4 and I5 and the lowermost roll I6 which is also an engraved metallic roll. lThe journals Il of roll I6 are supported by and adapted to rotate in bearing blocks I8 which are rigidly attached to the framework and foundation (not shown) of the machine. The weight of rolls I9, l2, I3, Ill, and I5, together with any pressure which may be applied to the journals of upper roll I9 by hydraulic cylinders II, or other pressure devices, is all carried by roll I9, as is apparent from the drawing, and is in turn, together with the weight of roll I6, carried by the journals I'I and bearing blocks I8.

The paper web 20 from unwinder roll 2 I which may be provided with the customary braking devices not shown, passes around tensioning rolls 22, ii desired, into the nip between yieldingsurfaced roll I 2 and engraved roll I3, thence around a guide roll 23 and into the nip between yielding-surfaced roll I5 and engraved roll i6, from which it is drawn by a known type of winding device, and rewound into a roll at' 2d.

The drive is applied, preferably, to roll I6 by any suitable driving mechanism, which for purposes of illustration is indicated as a beltv 36 driven by a motor 3l. The Winding device is indicated as driven in a well known manner from roll I6 by a belt 32 which is controlled to provide the proper' draw on paper web 20 by an adjustable idler 33. The particular driving devices used form no part of the present invention and may be replaced with any of the known devices for these purposes.

While the arrangement illustrated is at present deemed preferable under most conditions, it will be readily understood that the number and arrangement of the rolls can be altered in a variety of ways without departing from the present invention. For example, if the calender be narrow and roll I2 has sufficiently strong journals, is of adequate stiffness, and of a diameter such that the pattern does not repeat on successive revolutions, the upper roll I0 may in some cases be eliminated. If desired for any reason, more than two rolls can be used between the engraved rolls I3 and I6. So long as the number of rolls between them is even, the web will feed through both nips in the right direction and be embossed on opposite sides. Also additional rolls can be placed above roll I0 or below roll I6, if desired, and if roll I6 should be the third roll from the bottom, the drive could be applied either to it or to the bottom roll.

It is also possible, though not generally most desirable, to run the paper upward .instead of downward through the calender provided the drive be applied to the roll embossing the second side, or nearer to it than to that embossing the rstside. The pressure per linear inch in the second embossing nip is then less instead of greater than that in the first embossing nip. The second (then the upper) embossing roll must, I rind. still be larger than the irst, though not as much larger as when it is in the lower position Where its size must compensate for the higher pressure in the lower nip.

The primary points to be remembered are that only a yielding-surfaced roll dare contact either of the engraved embossing rolls on either side; that the two engraved rolls must be separated by an even number of rolls; that the roll used to emboss the second side must be materially larger in diameter than that used to emboss the first side; that the driving power must be applied either to the engraved roll embossing the second side, or nearer to that roll than to the engraved roll embossing the first side; and that when these conditions are fulfilled, the prominence of the embossing on the second side relative to that on the first side will be increased by increasing the applied pressure and decreased by decreasing the applied pressure.

The term engraved is herein used to denne a roll carrying a pattern in relief on its surface, and is not in any sense to be understood as imposing any limitation on the manner in which the pattern may have been formed on the metallic surface.

As has been seen the present invention makes it possible to emboss both sides of a paper web in a single passage through a single machine with a single drive and single pressure applying device, and to adjust the relative intensity of the embossing on the opposite sides to avoid twosidedness in the linished product. It thereby becomes possible, without sacrificing quality, to n secure output of two-side embossed paper on one machine the same as or higher than has heretofore been secured on two machines. Space, investment, labor, and waste are thereby saved and the cost of two-side embossing is materially reduced.

I claim:

1. In a calender comprising a plurality or" metallic and cooperating yielding-surfaced nonmetallic rolls, arranged in superposed contacting relationship to form a single stack; means for applying downward pressure to the journals of the uppermost roll, and means for supportingr the journals of the lowermost roll, in said stack; and means for positively rotating the lowermost roll in said stack; the improvement which adapts said calender for embossing a paper web on both sides in a single pass through said stack, said improvement comprising: an engraved pattern on the p surface of each of two of said metallic rolls, said engraved rolls contacting only yielding-surfaced rolls, and being separated from each other by an even number of rolls, the diameter of the lower of said engraved rolls being not less than two times that of the other of said engraved rolls.

2. The calender of claim 1 wherein the lower engraved roll is the positively rotated lowermost rol in the stack, and the upper engraved roll is the fourth roll from the bottom of the stack.

PAUL R. ILLNER.

REFERENCES CITED The following references are of record in the 

